In rotating machinery, the passages between fixed structures surrounding rotating components provide pathways for leakage of either the working fluid or support-system fluids. These pathways may allow support-system fluids, such as lubricating oil, to leak into the working fluid, or may allow the working fluid to leak into these support systems. These leaks along the shaft, or rotor, of the rotating machinery result in lower operating efficiency and quicker degradation of machine components, thereby requiring shorter maintenance intervals and more frequent replacement of parts.
To inhibit leakage through these pathways, rotating machines use various types of seals and sealing techniques. Circumferential seals, one type of these seals, are commonly used to prevent fluid leakage between compartments of the machine. Specific types of circumferential seals include controlled-gap seals, arch-bound circumferential seals, and segmented circumferential contacting seals. Each of these types of seals comprise a rotating component called a “seal rotor,” also known as a “runner,” and a non-rotating component called a “ring seal” or “circumferential seal.”
A common circumferential seal configuration comprises a seal rotor composed of a metallic material and a ring seal composed of carbon. This configuration exhibits a high degree of friction between the metallic rotor and the radially inner surface of the carbon ring seal. This friction wears the carbon seal quickly, resulting in the need for more frequent inspection and replacement. To avoid this friction at the sealing interface, a circumferential seal may be designed such that a small gap exists between the metallic seal rotor and the carbon seal. However, differences between the coefficients of thermal expansion (CTE) of the metallic seal rotor and the carbon ring seal will affect the size of the rotor-seal gap over the range of machine operating temperatures. Additionally, the metallic seal rotor will undergo mechanical growth due to centrifugal effects, further complicating control of the size of the gap between the seal rotor and ring seal. Consequently, the gap between the rotor and seal may be too large to efficiently seal the machine, or too small resulting in excessive wear to the carbon seal inner diameter and losses in machine efficiency.
A solution to excessively high seal wear or large rotor-seal gaps is to replace the metallic seal rotor (or, runner) with a ceramic runner. A ceramic runner may be chosen with a CTE closer to that of the carbon ring seal than the CTE of a metallic runner to mitigate the effects of thermal expansion. Ceramic may also experience less the mechanical growth from to centrifugal effects because ceramic may have a higher stiffness-to-weight ratio than a metallic compound. The thermal expansion and stiffness-to-weight ratio of ceramic materials allow tighter gaps to be maintained over the operating range of the machine, thereby avoiding some of the above the consequences of using a metallic rotor. Additionally, the use of a ceramic material result in a lower frictional force between the runner and the carbon ring seal, particularly when the ceramic runner sealing surface is lapped. In fact, the ceramic material may have a sufficiently low frictional force with the carbon seal that the two may be in contact during operation without significant wear to the seal or excessively large decreases in machine operating efficiency.
However, the use of ceramic materials imposes other design challenges, particularly in high-temperature applications, such as a jet engine. The circumferential seal runner must circumscribe and be affixed to, directly or indirectly, the shaft of the machine. This shaft is likely to be made of metal. Differences between the material properties of the ceramic and metallic machine components will result in varying stresses on the ceramic component during operating of the machine. These properties may include the CTE of the shaft and the runner materials, resulting in different rates of thermal expansion as temperatures change during machine operations. Other properties include the stiffness-to-weigh ratios of these materials, which produce differing rates and amounts of mechanical growth as the machine rotates. Additional stresses may be caused the assembly of the machine. Some rotating machines are assembled such that subcomponents are axially stacked upon one another around the shaft and groups of subcomponents may be held together by large compressive forces. This method of assembly is known as “lockup assembly.” These large compressive forces can create tensile stresses in portions of a ceramic runner. Ceramics may crack under these tensile stresses because they are brittle in nature.
FIG. 1 illustrates a cross-sectional, axial view of a prior art circumferential seal 100. The seal 100 comprises ceramic runner 106 which sealingly engages a carbon ring seal (not shown). The axial and radial alignment of ceramic runner 106 is maintained about shaft 104 by annular clamping members 108 and 110. These annular clamping members 108 and 110 are disposed between parts 116 and 114. Part 116 may be a bearing race or other clamped component, or part 116 may be a threaded nut used to supply a clamping force used to secure annular clamping members 108 and 110 to the shaft 104. The clamping force caused by, or transmitted through, part 116 may pass through an optional spacer 114 to a shoulder 112 of the shaft 104. Shaft 104 rotates about axis 102.
The ceramic runner 106 includes a radially inward extending flange from a main cylindrical body which engages the clamping members 108 and 110. This flange is adapted to receive the clamping force transmitted between the annular clamping members. Clamping member 110 has a length and thickness which allows for some radial flexibility. The annular member 108 may include circumferentially extending slots (not shown) which allow the annular member 108 to expand and contract, thereby imparting axial flexibility.
FIG. 2 illustrates a cross-sectional, axial view of another prior art circumferential seal 200. Seal 200 comprises a ceramic runner 206 which sealingly engages a carbon seal (not shown). Runner 206 is fixed to shaft 204 via clamp members 208 and 210. Clamp member 210 has a length and thickness designed to impart radial flexibility. Clamp member 208 retains an axial spring 218. The axial spring 218 provides an axial clamping force on runner 206. Clamp members 208 and 210 may be maintained in axial alignment along the shaft 204 by parts 214 and 216, which may be similar to parts 114 and 116 described above. Shaft 204 rotates about an axis 202.
While above circumferential seals provide a means for mounting a ceramic runner to a shaft, the smaller CTE of a ceramic runner compared to that of the metallic mounting components and the metallic shaft, as well as the low flexural strength of the ceramic runner, still present problems during the operation of the machine. First, the use of slots on axial support members, or springs between an axial support member and the ceramic runner provide additional leakage pathways. Second, as the temperature of machine rises, the metallic support members will expand more than the ceramic runner; due to the particular designs used in prior systems, the greater expansion of the metal components will increase the stress in the ceramic runner. Third, the runners illustrated in the above figures each require a radially inward extending flange to which the mounting components are engaged. This increases the complexity of the runner design.
Analysis of prior art sealing systems has revealed that the clamping loads generated during assembly of the machine may result in deflections of the individual components. Additionally, the centrifugal forces resulting from rotation of the shaft to which components are applied mounted may cause further deflections. These deflections result in undesirable line-contact loads that increase the risk of failure of the ceramic part and the wear rate of the contacting metal parts.
In accordance with some embodiments of the present disclosure, a circumferential seal for a machine having a rotating shaft is provided. The seal may comprise a sealing runner and a mounting element. The sealing runner may have a radially inward facing surface which extends axially along the shaft. The mounting element may comprise a support ring, a radial pilot, an axial flange, an isolating element, and a spring element. The support ring may have a radially outward facing surface which extends axially along the shaft a distance greater than the radially inward facing surface of the sealing runner. The radial pilot may extend radially outward from the support ring, and an axial flange may radially extend from the radial pilot to provide a surface which engages the runner on one end. A spring element may be provided to transmit a clamping force to the runner to maintain the runner in axial alignment. An isolating element may be provided between the runner and the spring element. In some embodiments, the runner and the support ring define a radially compliant opening to accommodate the relative thermal growth between the ceramic and metallic components without overstressing either. The runner may be ceramic and the mounting element may be metallic.
In accordance with some embodiments of the present disclosure, a circumferential seal for a machine having a rotating shaft is provided. The seal may comprise a sealing runner and a mounting element. The sealing runner may have a radially inward facing surface that extends axially along the shaft. The mounting element may be affixed around the circumference of the shaft, and may comprise a support ring, an axial flange, a radial pilot, and isolating element and a spring element. The support ring may form a radially outward facing surface that extends axially along the shaft a distance greater than the radially inward facing surface of the sealing runner. The radial pilot may extend radial outward from the support ring and may be configured to maintain the sealing runner in radial alignment. The axial flange may extend radially outward from the radial pilot. The isolating element may be in contact with a first axial end of the sealing runner. The spring element may be disposed proximate to the first axial end and may transmit a force through the isolating element to the sealing runner to clamp the sealing runner between the isolating element and the axial flange to maintain the sealing runner in axial alignment.
In accordance with some embodiments of the present disclosure, a circumferential seal for a machine with a metallic rotating shaft is provided. The seal may comprise a ceramic sealing runner and a mounting element. The ceramic sealing runner may have a radially inward facing cylindrical surface that may extend axially along the shaft. The mounting element may be affixed around a circumference of the shaft and may comprise a support ring, a radial pilot, an axial cylindrical flange, a cylindrical washer and a Belleville washer. The support ring may form a radially outward facing cylindrical surface that extends axially along the shaft a distance greater than the radially inward facing cylindrical surface of the ceramic sealing runner. The radial pilot may extend radially outward from the support ring to engage a first axial end of the ceramic sealing runner and may be configured to maintain the ceramic sealing runner in radial alignment. The axial cylindrical flange may extend radially outward from the radial pilot. The cylindrical washer may be in contact with a second axial end of the ceramic sealing runner. The Belleville washer may be disposed proximate to the second axial end and may transmit a force through the cylindrical washer the ceramic sealing runner to clamp the ceramic sealing runner between the cylindrical washer and the axial cylindrical flange to maintain the ceramic sealing runner in axial alignment.
In accordance with some embodiments of the present disclosure, a method of mounting a ceramic seal runner in a rotating machine is provided. The method may comprise providing a seal runner, providing a mounting element, engaging a first axial end of the seal runner, engaging a second axial end of the seal runner, and engaging an isolating element with a spring element. The seal runner may have a radially inward facing surface extending along a shaft of the machine. The mounting element may extend along the shaft of the machine and may have a support ring, a radial pilot, an axial flange, a spring element and an isolating element. The support ring may form a radially outward facing surface facing the radially inward facing surface of the seal runner. The radial pilot may extend radially outward form the support ring. The axial flange may extend radially outward from the radial pilot. The first axial end of the seal runner may engage with the isolating element. The second axial end of the seal runner may engage with axial flange and the radial pilot. The isolating element may engage with the spring element such that a compressive force is transmitted through the isolating element and seal runner to the axial flange, thereby maintaining an axial alignment of the seal runner relative to the shaft. The radial pilot may maintained a radial alignment of the seal runner about the shaft.
These and many other advantages of the present subject matter will be readily apparent to one skilled in the art to which the disclosure pertains from a perusal of the claims, the appended drawings, and the following detailed description of preferred embodiments.
While the present disclosure is susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and will be described in detail herein. It should be understood, however, that the present disclosure is not intended to be limited to the particular forms disclosed. Rather, the present disclosure is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the disclosure as defined by the appended claims.